Solution behaviour of mixed ligand complexes of nickel(II) involving penicillin group drugs and sulfur containing ligands under physiological conditions

摘要

Analysis of the pH-titration data obtained in aqueous perchlorate medium at 37 deg and I = 0.15 mol dm~(-3) (NaClO_4) for Ni~II-A-B- mixed ligand systems [A = 6apa or amp; B = cys, smc, pen or cya] shows the presence of mixed ligand complex species NiABH, NiAB and/or NiAB_(-1)B in addition to various binary species due to ligands A and B. The pK_NiABH~H values obtained in all these systems are close to each other, indicating the site of protonation in the NiABH species to be with ligand A. In the NiAB type of complexes, coordination of the ligand A results in the formation of a five-membered ring. In the NiAB_(-1)B species in the Ni~II-amp(A)-B systems, deprotonated AH_(-1) ligand binds the metal in a tridentate manner. In all the mixed ligand complexes, cys, smc, pen and cya(B) ligands are bidentate. The statistical parameter #DELTA# log K calculated indicates preferential formation and enhanced stability for the mixed ligand complexes relative to the binary one.